When Windows is activated, MS
records certain hardware info. The first computer you installed XP on and activated is the one they will have "on file", and if there are too many hardware changes on their point scale the next time that cd is used, and the activation process begins, you will have to call MS
again, explain yourself, and beg for mercy. After 30 days, the second computer you installed XP on will boot to an activation screen, and go no further. Since you know you can't legally activate the second installation, best to get all the data off of that computer before the 30 days is up.